For example, DE102008040318A1 teaches a rotational position sensing apparatus, which senses a rotational position of a rotatable body, more specifically a rotational position of a rotor of an electric motor.
This rotational position sensing apparatus includes a rotational position sensing magnet, a fixing member and a magnetic sensor. The rotational position sensing magnet generates a magnetic flux, which is used for sensing the rotational position of the rotor with the magnetic sensor. The fixing member holds the rotational position sensing magnet and is configured into a cylindrical cup form. The fixing member is fixed to an inner race of a bearing that rotatably supports the rotor. The fixing member includes a peripheral wall portion, a bottom wall portion and a projection (a ridge). The peripheral wall portion is configured into a cylindrical tubular form and defines a space, in which the rotational position sensing magnet is held. The bottom wall portion is configured into an annular form and radially inwardly projects from an axial end part of the peripheral wall portion. The bottom wall portion cooperates with the peripheral wall portion to define the space, in which the rotational position sensing magnet is held. The projection limits detachment of the rotational position sensing magnet from the fixing member. The projection circumferentially extends along an inner peripheral surface of the peripheral wall portion all around the inner peripheral surface. Furthermore, the projection radially inwardly projects from the inner peripheral surface of the peripheral wall portion. The rotational position sensing magnet is formed in the space, which is defined by the peripheral wall portion and the bottom wall portion. The magnetic sensor is placed at a corresponding location, which is axially opposed to an axial end surface of the rotational position sensing magnet.
A method of forming the projection along the inner peripheral surface of the peripheral wall portion all around the inner peripheral surface may include a press working process. In the case where the projection is formed by the press working process, since the projection circumferentially extends along the inner peripheral surface of the peripheral wall portion all around the inner peripheral surface, the peripheral wall portion needs to be separately formed from the bottom wall portion in order to install and remove the peripheral wall portion relative to a press-working die. In this case, after the forming of the projection along the inner peripheral surface of the peripheral wall portion through the press-working process, the bottom wall portion needs to be joined to an axial end part of the peripheral wall portion. Therefore, the number of the manufacturing steps is increased, thereby resulting in an increase in the manufacturing costs.
A method of forming the projection along the inner peripheral surface of the peripheral wall portion all around the inner peripheral surface without the need for the separating of the peripheral wall portion from the bottom wall portion may include a machining process (cutting/scraping, which involves removal of a material) or a hydroforming process. However, in the case where the projection is formed in the fixing member through the machining process, the processing time is relatively long, and thereby the fixing member cannot be formed at low costs. Furthermore, in the case where the projection is formed in the fixing member through the hydroforming process, an advanced forming technology is required, and thereby the fixing member cannot be formed at the low costs.